Variable Sexuality

Last month was Women’s History Month, which reminded me that one of the first researchers that wrote a study on cannabis was Sister Mary Etienne Tibeau. She was associated with Mount Mercy Junior College of Cedar Rapids, Iowa and wrote a research paper entitled Time Factor in Utilization of Mineral Nutrients by Hemp (1936). I honored her in the first book I wrote, and I recently decided to take another look at her article.

Tibeau chose hemp for experimentation “because it shows marked sexual dimorphism (marked differences between the sexes) and grows well under laboratory conditions.” In her research, she performed three experiments.

The first was “a series in which the plants were supplied with a high content of the essential elements K, Mg, Ca and N [potassium, magnesium, calcium and nitrogen] added to a Knop’s solution (a standard laboratory fertilizer solution)”.

Her second experiment was “a deficiency series in which the plants were supplied with a nutrient solution in which K, Mg, Ca and N respectively were omitted from the complete solution.”

The third experiment was “a series in which the plants after first undergoing periods of starvation of a single element were then supplied with a nutrient solution having a high content of this element.” Plants were starved of nitrogen for 27, 44 and 58 days.

The results of her experiments caught my eye as I reread the report again, specifically regarding her experiments with nitrogen. She wrote, “The most striking contrast was between the plants supplied with a high N solution and those supplied with an N-deficient solution. The plants that were given eight times the normal amount of N produced an abundance of dark green foliage, and all plants had begun to differentiate into females before they wilted and died.”

Her results continued to elaborate on the effects of nitrogen on her plants. “After an initial shortage of 27 days, plants were able to utilize available N (supplied in high amounts) and the plants were all females. After an initial starvation of 44 days, the plants were unable to adequately use N (supplied in high amounts) and male plants resulted. The plants starved of N for 58 days had already differentiated into males when N was supplied. After 64 days they were still hardy, growing slowly as males plants.”

I decided to duplicate that portion of her experiment and see if plant sex could be manipulated by N availability to the plant. The experiment consists of 40 cups with seeds planted. They are divided into three groups that will include only 10 cups each. One group, the control, is supplied with a fertilizer containing equal amounts of N-P-K. A second group is given fertilizers with. The second group is provided with fertilizer containing only P-K. The third group is supplied N-P-K, but the N is oversupplied by a factor of 8 until the plants indicate sexuality. In addition to the seedlings, 10 clones purchased at a store and already identified as female will be included. Five each will be added to the N starved group and the N oversupplied group.

Tibeau kept the seeds/seedlings under constant light for 12 days. She then transferred them to natural light on May 27. On May 27, dawn to dusk in Cedar Rapids, Iowa lasts 16 hours, two minutes, a long enough light regimen to promote vegetative growth.

In this experiment, the seeds/seedlings will have continuous light for 14 days. Then they will be provided with 16 hours of light for 14 days. They are being provided with 12 hours of light daily; a long enough dark period to promote flowering.

The Results So Far:

Seeds and clones were placed in cups filled with coir that had been soaked and rinsed to remove any nutrients. They were placed in a space with a light regimen of 16 hours and will remain there for another 13 days. Upon germinating, they will be irrigated with nutrient-water solution.